About S.K.

P. Silva

Postgraduate Institute of Agriculture, University of Peradeniya, LK

About P.

Abstract

Understanding relationships between population density and habitat quality are crucial in bird conservation attempts. The present study was conducted to document the densities of Sri Lanka White-Eye (Zosterops ceylonensis) (SLWE) and Oriental White-Eye (Z. palpebrosus) (OWE) in solitary and co-existence situations. Censuses of the two white-eye species were conducted in their allopatric and sympatric zones, between September 2017 and June 2019. The allopatric ranges of both species acted as ‘controls’ for this experiment. Analysis of covariance was used to capture the changes in densities in zones of allopatry whereas, correlation test was done to analyze density changes in sympatric zone. Results showed that there was a marked decline in density of OWE from the end of its allopatric zone to the beginning of sympatric zone. SLWE showed no such change. One-way ANOVA showed that the changes in densities with elevation were significant (P<0.01), which was supported by the analysis of covariance (P<0.01). A significant negative correlation (P<0.01) of density in sympatry with increasing elevation was observed for OWE while SLWE showed no significant correlation between density and elevation, and no negative correlation of densities in sympatry. Association of density of OWE with changes in habitat with elevation was suggested as one possibility since forest structure alone does not limit the distribution of OWE according to its pattern on distribution in India where OWE is the sole white-eye species. Previous studies have also shown that at least one of these species show some character displacement in the sympatric zone. Thus, it can be inferred that SLWE has evolved with sufficient differences for ecological isolation from OWE. This has resulted in ecological release to certain extent where OWE must have been replaced with changes in vegetation structure together with competition from its congeneric species.